public static bool ScreenToBoard(Camera cam, LibFever.Grid grille, Vector3 mouse_pos, LayerMask mask, out DataStructures.Point board_index)
    {
        RaycastHit hit;
        Ray        ray = cam.ScreenPointToRay(mouse_pos);

        if (Physics.Raycast(ray, out hit, 100.0f, mask))
        {
            Debug.Log("hit : " + hit.point);
            board_index = LibFever.Grid.getCaseIndex(grille, hit.point);
            Debug.Log("index : " + board_index);
            return(true);
        }
        board_index = new DataStructures.Point(-1, -1);
        return(false);
    }